Fresh meat and fish are nutritious but highly perishable foods. During production and storage they are exposed to unavoidable microbial contamination from the processing environment. Such contamination may include spoilage organisms and pathogens. It is therefore a priority for food processors to restrict the growth of contaminants so that they do not develop to potentially dangerous levels. One of the methods employed is the use of safe bacteria to curb growth of spoilage and disease-causing micro-organisms. The meat-borne lactic acid bacterium Lactobacillus sakei shows in this view excellent properties.
L. sakei has the ability to survive and grow on fresh meat, forming the dominant population when selective techniques are applied. Some strains are widely used in Europe for artisanal and larger scale manufacture of fermented sausages because of their useful preservative properties. But they could also be used as meat biopreservative by preventing the growth of unwanted bacteria (Vermeiren et al. 2004 Int. J. Food Microbiol. 96:149-164).
Strains of L. sakei can display an important variability in phenotypic traits and have for long been considered difficult to classify. Previous studies have disclosed approaches for L. sakei strains classification. Studies using numerical analysis of RAPD patterns (Berthier and Ehrlich 1999 Int. J. Syst. Bacteriol. 49:997-1007) or SDS-PAGE soluble protein content patterns have suggested the division of the strains into two subgroups, although weakly defined and not comparable according to the studies.
Thus, L. sakei strains classification obtained through these approaches remains unsatisfactory. An aim of the present invention is to provide better methods of classification, characterization and identification of L. sakei strains, which could in particular be used to identify L. sakei strains present on food or in a cocktail of bacteria used as biopreservative.
The inventors of the present invention have herein identified, based on an in silico study of the L. sakei genome and on experimental validation on a large collection of L. sakei strains, a combination of markers for characterizing and detecting these strains. In particular, 29 marker genes have been isolated, whose combination provides an optimal way of characterizing L. sakei strains.